Predictive video encoding procedures use areas of an image already transmitted to estimate the current image information and calculate a prediction error which deviates therefrom. As a rule, the current image information is determined from the image areas already transmitted by dividing the current input image into blocks and by looking for blocks in previous images that correspond to each of these blocks, which minimizes the extent of an error or a gap. The block image constructed in this way is subtracted from the current input image and the prediction error thus calculated is transformed via a discrete cosine transformation or an integer transformation from the local into the frequency range. The transformed prediction error data is then quantized and the coefficients thus produced are compressed and sent to the recipient by a Context Adaptive Binary Arithmetic Coder (CABAC).
For arithmetic encoding, the coefficients contained in the prediction error matrix are linearized by coefficient sampling and converted into a series of levels and lengths of zero sequences. Both the level values and the length values are represented here as unary values and encoded independently of each other bit-by-bit. The leading signs of the levels are encoded separately. For encoding the level values, a specific context is used in each case for the first two bits and a further specific context is used for all following bits. Context in this connection should be understood as the distribution of the frequencies of the logical 0s and 1s. The context thus specifies the likelihood that a bit is set or not set. For encoding the length values, a specific context is used for the first bit and a further specific context is used for all following bits. A separate context is also used for encoding the leading sign which is represented by a individual bit. The six specific contexts used together make up a context set.
Using this prior art as a starting point, an object of the present invention is to further improve context-adaptive binary arithmetic encoding.